add some rdoc

* add reference to spawn to fork
* add an example which runs ruby

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41043 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* lib/cgi/cookie.rb (inspect): add inspect for debug.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41044 b2dd03c8-39d4-4d8f-98ff-823fe69b080e